Two new species of the millipede genus Tylopus Jeekel, 1968 from Shan State, Myanmar (Diplopoda, Polydesmida, Paradoxosomatidae)

Abstract The predominantly Indochinese to southern Chinese millipede genus Tylopus presently comprises 76 described species, including two new, T. monticolasp. nov. and T. sutcharitisp. nov., both described and illustrated based on material from a limestone mountain in Taunggyi District, Shan State, Myanmar. Both new species have been found to occur syntopically near limestone caves and are assumed to be narrowly endemic to the Taunggyi Mountains, southwestern Shan State, Myanmar. A key to all six Tylopus species known to occur in Myanmar is provided, and their distributions are also mapped.


Introduction
The predominantly Indochinese to southern Chinese millipede genus Tylopus Jeekel, 1968, has long been recognized as one of the most speciose and widespread not only within the family Paradoxosomatidae, but also in the entire class Diplopoda (Likhitrakarn et al. 2010(Likhitrakarn et al. , 2016Golovatch 2019). This genus, formerly known as Agnesia Attems, 1953, has been reviewed and rediagnosed several times (Jeekel 1965(Jeekel , 1968Golovatch and Enghoff 1993;Likhitrakarn et al. 2010), but most taxonomic works have focused on adding new species descriptions, presenting a key and a distribution map to reveal the high diversity of the genus (Nguyen 2012;Liu and Luo 2013, Golovatch 2013, 2014, 2018, 2019, 2020Likhitrakarn et al. 2014Likhitrakarn et al. , 2016. At the moment, 74 species of Tylopus are known from Indochina and the adjacent parts of southern China and Myanmar (formerly Burma). Most of the known species diversity of Tylopus is encountered in Thailand and Vietnam.
Myanmar forms part of the Indo-Burma biodiversity hotspot (Myers et al. 2000;Sodhi et al. 2004). It supports extremely high biodiversity and abundant natural resources, including millipedes (Diplopoda). At present, Myanmar's known millipede diversity has gradually been revealed to amount to 96 species from 36 genera, 13 families and eight orders, containing 74 endemic and only five widespread synanthropic species (Likhitrakarn et al. 2017(Likhitrakarn et al. , 2018Pimvichai et al. 2018;Srisonchai et al. 2018a, b). Furthermore, there are 527 millipede records from Burmese amber (Burmite; Cretaceous, ca 100 Mya), representing 13 of the 16 extant orders. Only the orders Sphaerotheriida, Julida and Siphonocryptida have not yet been reported from Burmite. Against this background, no fossil of the family Paradoxosomatidae, one of the largest and most diverse in the entire class Diplopoda globally, has previously been recorded from Myanmar (Wesener and Moritz 2018).
Four Tylopus species, all endemic, have been found in Myanmar. The first two species of Tylopus to be revealed from that country were Tylopus doriae (Pocock, 1895) and T. silvestris (Pocock, 1895), both described by Pocock (1895). It was 120+ years later that two further species were added: T. brehieri Golovatch, VandenSpiegel & Semenyuk, 2016and T. punctus Likhitrakarn, Golovatch & Panha, 2016Likhitrakarn et al. 2016). Myanmar's climate, geology, topography and, partly, its biota are very similar to those of the neighbouring Thailand; consequently the Tylopus species diversity in Myanmar is surprisingly low compared to Thailand with its 31 species. This is undoubtedly due to many areas of Myanmar still being difficult to access, remaining poorly collected and often even dangerous, coupled with local natural history research being rudimentary and secluded. Hardly surprisingly, the arthropod fauna of Myanmar is poorly known and understudied. Studies on the millipede diversity of Myanmar have recently resumed since the British colonial times, chiefly due to the activities of the Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand, headed by one of us (SP).
The present paper puts on record two new species of Tylopus collected from a limestone mountain in the Taunggyi District, southwestern Shan State, Myanmar. A key to and updated distributions of all six species of Tylopus currently known to occur in Myanmar are also provided.

Materials and methods
New material was collected in Myanmar, especially in limestone mountain areas, with the support of Fauna & Flora International (FFI) in 2015-2017, collaborating with the Animal Systematics Research Unit (ASRU), Chulalongkorn University. The collecting activities took place under the limestone conservation projects which aim to protect biodiversity in limestone habitats (Grismer et al. 2018a, b, c;Fauna & Flora International 2021).
Live animals were photographed in the laboratory using a Nikon 700D digital camera with a Nikon AF-S VR 105 mm macro lens. Specimens were preserved in 75% ethanol, and morphological observations were carried out in the laboratory using an Olympus stereo microscope. Scanning electron micrographs (SEM) of gonopods coated with gold were taken using a JEOL, JSM-5410 LV microscope, returned to alcohol after SEM examination. Digital images of the specimens were taken in the laboratory and assembled using the "Cell D " automontage software of the Olympus Soft Imaging Solution GmbH package. In addition, line drawings of gonopod characters were also prepared. Both holotypes, as well as most of the paratypes are housed in the Museum of Zoology, Chulalongkorn University (CUMZ), Bangkok, Thailand; some paratypes are donated to the collection of the Zoological Museum, State University of Moscow (ZMUM), Russia, as indicated in the text.
Collecting sites were located by GPS using the WGS84 datum. The distribution maps of all Tylopus species recorded from Myanmar were executed using QGIS 3.18.0 (QGIS Development Team 2021). Google satellite maps were downloaded via the QuickMapServices plugin. The images were enhanced and arranged in plates with Adobe Photoshop CS6 software.
In the synonymy sections, D stands for the original description and/or subsequent descriptive notes, K for the appearance in a key, L for the appearance in a species list, and M for a mention.
Colouration of live animals dark brown (Fig. 1A); calluses of paraterga, venter and legs lighter brown; colouration of alcohol material after two years of preservation faded to dark brown; head, antennae and tip of epiproct light brown, calluses of paraterga yellowish brown to pallid, venter and legs light brown to light yellowish (Fig. 2).
Name. To emphasize the habitats where this new species was discovered; "monticola" meaning a mountain-dweller or a highlander; noun in apposition.
Remark. The species was found quite far away (about 120 air-km) from the type locality of the most similar species, T. rugosus Golovatch & Enghoff, 1993 (Fig. 9). Both new species described here have been found to occur syntopically. Diagnosis. This new species comes to a dead end in couplet 5 in the latest key to Tylopus species (Likhitrakarn et al. 2016), but it seems to be particularly similar to the later  described and grossly sympatric T. brehieri Golovatch, VandenSpiegel & Semenyuk, 2016, especially in its gonopod conformation. Both species compared come from Shan State, Myanmar ), but T. sutchariti sp. nov. differs in the presence of a small and triangular gonopod process h (vs. absent), and the large and subtrapeziform apicolateral lobe (l) with a smooth apical margin (Figs 6B, D, 7B) (vs. a subtriangular l with an apically rugose and denticulate margin), as well as the pleurosternal carinae being complete crests with a caudal tooth clearly visible until segments 16 (♂) or 13 (♀), thereafter missing (Fig. 5B, D, E) (vs. visible until segment 10), while the sternal lobe between ♂ coxae 4 is deeply notched (Fig. 5H, I) (vs. prominent and subquadrate).
Name. To honour Dr. Chirasak Sutcharit, Professor at the Department of Biology of the Chulalongkorn University, Bangkok, who participated in collecting the type series.
Remark. Both new species described here have been found to occur syntopically (Fig. 9).
Key to species of Tylopus currently known to occur in Myanmar, chiefly based on ♂ characters

Discussion
Of a total of 76 species of Tylopus presently known globally, including two new described above, most of the diversity (31 species, or >41%) comes from Thailand, followed by Vietnam (21 species), Laos (12 species), southern China (8 species) and Myanmar (6 species). Almost all Tylopus species appear to be confined to montane woodlands exceeding 500 m in elevation (Likhitrakarn et al. 2016). Furthermore, most of them (92%) are short-range endemics or confined to a small area (< 4000 km 2 ). Many species occur sympatrically, some even syntopically, but then they tend to differ in the timing of sexual maturity or mating season. For instance, the Doi Inthanon and Doi Suthep mountains, both in northern Thailand, support at least 10 congeners each (Likhitrakarn et al. 2014). Unfortunately, most of the known species (75%) have only been collected once and from a single locality. The genus Tylopus seems to be particularly similar to two genera of the large and mostly Asian tribe Sulciferini, viz. Oxidus Cook, 1911 andHedinomorpha Verhoeff, 1934. All three share the presence of a unique gonopodal apicolateral lobe (l) separated from the femorite by a more or less distinct, basal, (sub)transverse sulcus.  has recently discussed the morphological differences between these three genera, Tylopus being distinct primarily in the particularly elaborate gonopodal telopodite. The distinction of Tylopus from Oxidus has also been confirmed by molecular evidence (Nguyen et al. 2017).
In addition to putting on record two new, presumably narrowly endemic species of Tylopus from the Taunggyi Mountains, southwestern Shan State, Myanmar, and thus bringing the number of Tylopus spp. of Myanmar to a total of six, we map their distributions (Fig. 9). Only T. doriae has been recorded from two countries, Myanmar and Thailand, whereas the other five seem to be more strongly localized. Given that Myanmar remains one of the largest, but least-surveyed countries in the East Indies, and considering the large limestone montane areas it harbours, there can hardly be any doubt that more species of Tylopus will be found there in the future.